Bidirectional optical communication device and bidirectional optical communication apparatus

Abstract

A bidirectional optical communication device satisfies a condition of θ fb ≦0≦θ fa or θ fa ≦0≦θ fb when θ fa and θ fb are angles of inclination between an optical axis of an optical fiber and transmission light after incidence with a numerical aperture NA at an outermost periphery, and θ fa and θ fb are expressed as the follows: θ fa =Sin −1 [{n 0 Sin(θ L +Sin −1 ( NA )/ n 0 +θ T )}/ n f ]−θ T θ fb =Sin −1 [{n 0 Sin(θ L −Sin −1 ( NA )/ n 0 +θ T )}/ n f ]−θ T where n f and n o denote refractive indexes of a core of the optical fiber and air, respectively. The bidirectional optical communication device is capable of decreasing restraint of a transmission distance by reducing fluctuation of reception efficiency by the transmission distance and reducing interference between transmission light and reception light.

1. A bidirectional optical communication device for carrying out transmission and reception of an optical signal with use of one optical fiber having a curved end face as a transmission medium, comprising:
 a light emitting element for generating transmission light;  
 a collection member for collecting transmission light emitted from the light emitting element and coupling the transmission light to the optical fiber; and  
 a light receiving element for receiving reception light emitted from the optical fiber, wherein 
   θ fb ≦0≦θ fa  or θ fa ≦0≦θ fb    
 
 
     is satisfied when angles of inclination θ fa  and θ fb  between an optical axis of the optical fiber and the transmission light after entering the optical fiber with a numerical aperture NA at an outermost periphery are expressed as follows:
   θ fa =Sin −1   [{n   0  Sin(θ L +Sin −1 ( NA )/ n   0 +θ T )}/ n   f ]−θ T    
   θ fb =Sin −1   [{n   0  Sin(θ L −Sin −1 ( NA )/ n   0 +θ T )}/ n   f ]−θ T    
 
     where θ L  denotes an angle between an optical axis of transmission light prior to entering the optical fiber and an optical axis of the optical fiber, θ T  denotes an angle between a perpendicular line of the optical fiber end face in a position where the transmission light is coupled to the optical fiber and an optical axis of the optical fiber, NA denotes a numerical aperture of the transmission light collected by the collection member prior to entering the optical fiber, n f  denotes a refractive index of a core of the optical fiber, and n o  denotes a refractive index of space through which the transmission light passes prior to entering the optical fiber. 
   
   
     2. The bidirectional optical communication device as defined in  claim 1 ,
 wherein the transmission light enters the optical fiber end face with the optical axis of the transmission light inclined from a central axis side to a peripheral side of the optical fiber.  
 
   
   
     3. The bidirectional optical communication device as defined in  claim 1 , further comprising
 an optical path changing member disposed between the collection member and the optical fiber for changing an optical path of the transmission light so as to lead the transmission light to a position displaced from a center of the optical fiber end face in radial direction.  
 
   
   
     4. The bidirectional optical communication device as defined in  claim 3 ,
 wherein the optical path changing member is a prism for changing an optical path of the transmission light by refracting the transmission light.  
 
   
   
     5. The bidirectional optical communication device as defined in  claim 1 ,
 wherein the collection member has an optical path changing function for changing an optical path of the transmission light so as to lead the transmission light to a position displaced from a center of the optical fiber end face in radial direction.  
 
   
   
     6. The bidirectional optical communication device as defined in  claim 5 ,
 wherein the collection member is a concave-surfaced reflection mirror that collects the transmission light by changing an optical path of the transmission light with use of reflection of the transmission light.  
 
   
   
     7. A bidirectional optical communication apparatus having a plurality of bidirectional optical communication devices optically coupled to each end of an optical fiber for carrying out transmission and reception of an optical signal among a plurality of the bidirectional optical communication devices with use of the optical fiber as a transmission medium, wherein
 at least one of the plurality of the bidirectional optical communication devices is the bidirectional optical communication device as defined in  claim 1 .